The present invention relates to an apparatus for sealing packaging containers. More specifically, the present invention relates to an ultrasonic sealing apparatus for sealing packaging containers.
Packaging containers for holding liquid food such as milk, fresh beverages, and the like have been conventionally manufactured by processing packaging materials into specified container shapes. In the case of gable top cartons, such as the TETRA REX(copyright) carton, a carton blank cut to a specified shape and size, and longitudinally sealed together is typically manufactured on a packaging machine by erecting the blank into a cylindrical sleeve. The erected carton blank is then placed onto a mandrel for bottom forming and sealing. The partially formed carton is then placed on a conveyor for transport to additional processing stations on the packaging machine. A fitment may be attached at a processing station and the partially-formed carton may be sterilized at another processing station. The partially-formed carton is then filled with a desired liquid food product at a filling station. The filled carton is then transported to a top sealing station where the top panels of the carton are folded along specified creases and sealed together to form the finished formed, filled and sealed gable top carton.
In the case of a parallelepiped container such as the TETRA BRIK(copyright) package, a web of material is installed onto a vertical form, fill and seal machine. The web of material is longitudinally sealed to form a tube about a fill pipe on the machine. A transversal seal is made to the tube which is then filled with a desired liquid food product. A second transversal seal is made which also cuts the package from the entirety of the tube of material. The filled package is then folded and shaped to produce the ubiquitous TETRA BRIK(copyright) package.
For the above-mentioned packages, and other packages, the packaging material is usually composed of paperboard base material with both sides coated with a thermoplastic resin material such as polyethylene. Additionally, the paperboard base material may have a gas barrier layer which may also be coated with a thermoplastic resin material.
Several methods may be used to seal the packaging container on a packaging machine such as impulse sealing, hot air sealing and high frequency sealing. However, there are problems associated with the use of each of these methods.
The impulse sealing method has heat conducted through the paperboard base material. However, the thermal conductivity of the paperboard base material will vary with its water content. Therefore, the sealing parameters on the impulse sealing device must be adjusted with each different lot of paperboard base material and the storage conditions of the material. Such adjustments complicate the processing work and make it difficult to fabricate packaging containers in an orderly manner.
The hot air sealing method has hot air directed at specified locations of the thermoplastic resin material. The thermoplastic resin material is heated indirectly with hot air, making it impossible to control the temperature of the thermoplastic resin. Such a lack of temperature control results inconsistent seals on the packaging containers.
The high frequency sealing method requires the use of an aluminum layer as the gas barrier layer since the heat necessary to effectuate the seal is generated by high frequency waves transmitted to the aluminum layer. The necessity of the aluminum layer increases the cost of the packaging material.
Another sealing method is the use of ultrasonic energy which generates heat in the thermoplastic resin material through transmission of vibrations from an ultrasonic horn to the packaging material. The use of ultrasonic sealing negates the problem of varying water content in the paperboard base material since the thermoplastic resin is melted without regard to the thermal conductivity of the paperboard base material. This allows for a standardization of the sealing parameters on the packaging machine since adjustments for varying lots of paperboard base material and storage conditions are unnecessary. Further, the seals on the packaging containers are consistent since the thermoplastic resin material is directly heated, allowing for accurate control of the temperature. Finally, the need for an aluminum layer is negated since the seals are better (tighter, more reliable) thereby lowering the cost of the packaging material.
However, ultrasonic sealing is not without its own problems in the sealing of packaging containers. Ultrasonic sealing requires that the horn component be pressed uniformly against the sealing portions of the packaging material. When the packaging container is fabricated on the packaging machine, some sealing portions are formed with a single sealing line while other sealing portions are formed with overlapped sealing lines that cross over each other. A greater number of packaging material layers results in an increase in the overlapped portions, with a smaller number of single sealing line portions where there is no crossing over. Accordingly, the sealing pressure in the portion without the overlapping is a smaller force than in the overlapping sealing portions. This results in poor transmission of ultrasonic energy from the horn to the sealing portion of the packaging container, which results in insufficient heat generation, which results in poor or incomplete sealing of the sealing portions of the packaging container.
It is a primary object of the present invention to provide a novel apparatus and method to seal packaging containers with ultrasonic energy.
It is an additional object of the present invention to provide an apparatus and method for sealing packaging containers with uneven sealing portions.
It is an additional object of the present invention to provide an improved anvil for ultrasonic sealing.
One solution for the problems of the prior and the above-mentioned objectives is an apparatus for sealing packaging containers that includes an ultrasonic generator, a horn and an anvil with an abutting portion that deforms to correspond to the exterior shape of the sealing portion of the packaging container. The abutting portion may include a plurality of mutually slidable plates. Further, the apparatus may include an electromagnet for selectively restricting the sliding of each of the plates. Still further, each of the sliding plates may be composed of either a ferromagnetic material, paramagnetic material, ceramic material or any combination thereof.
Another solution is a method for sealing the sealing portions of a packaging container through using the afore-mentioned apparatus. In such a method, the plates are allowed to conform to the exterior shape of the sealing portion before the electromagnet is magnetized thereby restricting the movement of the slidable plates.
Yet another solution is an anvil for ultrasonic sealing that has an abutting portion that conforms to the exterior shape of the sealing portion of a container. The anvil may be composed of three blocks, with the abutting portion disposed on the middle block and an electromagnet disposed on either of the side blocks.